Variable compression ratio engine

ABSTRACT

The present invention is a variable compression ratio engine which can operate both in a Miller cycle and a normal cycle, and which can produce a high output, reduce the generation of NOx, and prevent the occurrence of knocking. For this purpose, the engine is provided with an exhaust gas recirculating device equipped with a first cam shaft (10), provided with cams (11, 12, 13) for operating an intake valve (2) and exhaust valves (4, 5), and a second cam shaft (20), provided with cams (21, 22) for operating at least one intake valve (3) and an exhaust valve (5) to thereby recirculate part of exhaust gas into intake gas.

TECHNICAL FIELD

The present invention relates to a variable compression ratio engine,and more particularly, to a variable compression ratio engine which canconvert between an ordinary cycle and a Miller cycle.

BACKGROUND ART

In order to reduce NOx contained in exhaust gas, exhaust gasrecirculation (EGR), by which exhaust gas, which is an inert gas, isrecirculated into an intake gas and by which the combustion temperatureis lowered, has been conventionally conducted in vehicle engines.Regarding this exhaust gas recirculation, when the load on an engine isheavy, the volume efficiency is improved as the temperature of EGR gasbecomes lower, and the combustion temperature becomes lower and the NOxdecreases as there is a larger amount of EGR gas. On the other hand,when the load on an engine is light, the combustion is not stable whenthe temperature of the EGR gas is low, so that an EGR gas with a hightemperature is preferable. For this reason, a method of controlling theEGR gas to be cooled when the load is heavy and of controlling the EGRgas so that the EGR gas is not cooled when the load is light, byproviding an EGR gas cooling means, is already known (for example, referto Japanese Patent Application Laid-open No. 4-175453 and JapanesePatent Application Laid-open No. 4-301172).

However, when the EGR is conducted with a heavy load, disadvantages ofincreased fuel consumption, reduced output, etc., are brought about.

In other conventional art, many of the compression ratios of engines,for example, direct injection type diesel engines are set in thevicinity of 15 to 17. This compression ratio is required for securingstarting efficiency and a good combustion state when a load is light,for example, a combustion state without blue and white smoke includinghydrocarbon compounds, etc. The times for opening and closing an intakevalve are fixed in order that the aforementioned compression ratio isobtained. When the compression ratio is determined, the pressure withina cylinder chamber at the end of the compression stroke is determined,and the pressures within the cylinder chamber at ignition, explosion,etc., are also determined. Meanwhile, a maximum allowable pressurewithin a cylinder chamber is determined in accordance with the engine,and the higher the compression ratio is, the higher the pressure withina cylinder chamber becomes at the end of compression. Accordingly, thedifference between this pressure within a cylinder chamber and themaximum allowable pressure within a cylinder chamber lessens, and thisis the main factor which prevents an engine from outputting high power.

The aforementioned compression ratio is desired to be in the vicinity of11 to 13, from the viewpoint of combustion efficiency and high poweroutput. As an example, average axial effective pressures, which can beachieved with the compression ratios at 17 and 12, are shown in FIG. 27.A unit of pressure in FIG. 27 is kgf/cm². For example, in the case of anengine with a maximum allowable pressure within the cylinder, Pmax, of150 kgf/cm² or less (Pmax≦150 kgf/cm²), the average axial effectivepressure stays at 21 kgf/cm² with the compression ratio of 17; but withthe compression ratio of 12, the average axial effective pressure can be34 kgf/cm², that is, high power can be outputted.

However, since it is an absolutely necessary condition to obtain anexcellent starting and an excellent combustion state when the load islight, in the current state, the compression ratio is set in thevicinity of 15 to 17 and high power output is sacrificed. This is alsothe case in gasoline engines, and though the compression ratio isdesired to be 11 to 13 as in the diesel engines from the view ofcombustion efficiency (thermal efficiency), the compression ratio is setat 8 to 10 in order to prevent the occurrence of knocking when the loadis heavy. As a result, there are disadvantages of increasing fuelconsumption and of generating a large amount of CO².

As the art which improves thermal efficiency of diesel engines and whichreduces exhaust emission, a Miller cycle engine, by which a lowcompression ratio and a high expansion ratio can be obtained, has beenknown. There are two types of Miller cycle engines; a type which blocksthe flow of intake gas in the middle of an intake stroke by closing anintake valve at an early stage, and a type which lets intake pressureescape at the beginning of a compression stroke by closing the intakevalve at a latter stage. However, as described above, when a Millercycle is operated at a low speed and in a light load range of theengine, the effective compression ratio is reduced, and therefore therehas been a disadvantage of unstable ignition.

As a means of eliminating this disadvantage, there is the Miller cycleengine described below (refer to, for example, Japanese PatentApplication Laid-open No. 63-277815). In FIG. 28, an intake valve 60 isopened and closed by the medium of a crankshaft, timing gear, cam shaft,tappet, push rod, and rocker arm, which are not illustrated in thedrawing. At the middle of an upstream passage 61 of the intake valve 60,a new valve 62 is provided, and the engine speed, a load, etc., aredetected as signals. Based on this detection, the valve 62 is closed,earlier than the intake valve 60 is closed, by a valve mechanism 63connecting to a conversion mechanism 64 according to the drivingconditions; in other words, an early closing Miller cycle operation isconducted. 66 is an exhaust valve, and 67 is a cylinder chamber. Thevalve 62 and the valve mechanism 63 may be rotary valves.

FIG. 29A and FIG. 29B show the relationship between the position of apiston (axis of abscissa) of the aforementioned engine and the area ofthe opening, and the curve A corresponds to the exhaust valve 66, thecurve B corresponds to the intake valve 60, and C, shown by two lines,corresponds to the valve 62. As shown in FIG. 29A, when the load islight, the intake valve 60 and the valve 62 open and close at the sametime, so that the area of the opening of the intake valve 60 isrepresented by the hatched portion, and the engine operates in a normalcycle. On the other hand, when the load is heavy, the valve 62 opens andcloses earlier, as much as S as FIG. 29B shows, and the actual openingarea of the intake valve 60 is represented by the hatched portion.Accordingly, the intake valve 60 closes early with the actualcompression ratio being low, so that the engine operates in an earlyclosing Miller cycle, and a high power can be outputted.

However, even if the valve 62 is closed by operating the engine in aMiller cycle as described above, the amount of air in the passage 65between the intake valve 60 and the valve 62 is added to the amount ofair in the cylinder 67 when the intake valve 60 opens. Accordingly thevolume increases, so that the effect of closing the valve 62 in themiddle of the intake stroke is decreased, and the effect of the Millercycle is reduced. There is a disadvantage of a pumping loss caused by anincrease of intake resistance immediately before the valve 62 closes andby the comings and goings of intake gas resulting from the amount of airin the passage 65 becoming an excessive volume.

Further, in each type of engine, it is an important art to make theopening and closing times of the valves variable in order to obtain hightorque generated over a large rotational range. For example, as apractical method of making a valve timing variable, a method of changinga phase of a timing gear and a cam shaft, by engaging the cam shaft withthe timing gear by the medium of a helical spline and by moving thetiming gear in an axial direction, has been known (refer to, forexample, Japanese Patent Application Laid-open No. 61-85515).

However, though high torque can be obtained over a wide range in theaforementioned structure, the angle variations of the cam shaft cannotnormally be made to be 20° to 40° or more at a crank angle, so that itis difficult to make a helical angle of the helical spline extremelylarge. Accordingly, in order to convert between a normal cycle (anOtto-cycle, a diesel cycle, etc.) and a Miller cycle by changing theopening and closing times of the valves in order to output high power,the angle variations of the cam shaft need to be 70° to 90° at the crankangle, and the conventional helical spline type is insufficient.

SUMMARY OF THE INVENTION

In order to eliminate the aforementioned disadvantages of theconventional art, an object of the present invention is to provide avariable compression ratio engine which can convert between a normalcycle and a Miller cycle, and which has a sufficient effect of a Millercycle. Another object is to always conduct a most suitable EGR over awide driving range of an engine by increasing the EGR rate (the amountof EGR gas supply) under a light load and by decreasing the EGR rateunder a heavy load.

The first aspect of the variable compression ratio engine relating tothe present invention is characterized by including an exhaust gasrecirculating device equipped with a first cam shaft, provided with camsfor operating an intake valve and exhaust valves, and a second camshaft, provided with cams for operating at least one intake valve and anexhaust valve, and by including a valve driving device by which theclosing time of the intake valves in the intake stroke at a specifieddriving time, is set at a time before a piston is at the bottom deadcenter, with the opening and closing times of the exhaust valve beingset at a time when the piston is in the vicinity of the top dead center;and by which, in the intake stroke under a light load, the closing timeof at least one intake valve is set at a time when the piston is in thevicinity of the bottom dead center, with the opening and closing timesof the exhaust valve being set at a time before the piston is at thebottom dead center, to thereby recirculate part of the exhaust gas intointake gas when a load is light, by changing the phase of the cams onthe second cam shaft by the valve driving device, in a variablecompression ratio engine which is provided with at least two intakevalves and at least one exhaust valve per cylinder and which changes thecompression ratio by opening and closing the intake valves and/or the atleast one exhaust valve by cams provided on at least two cam shafts (thepresent structure shall be the first setting of the opening and closingtimes of the valves).

The aforementioned valve driving device can be a valve driving device bywhich, in the intake stroke under a light load, the closing time of theintake valves can be set at a time when the piston is in the vicinity ofthe bottom dead center, with the opening and closing times of theexhaust valve being set at a time before the piston is at the bottomdead center, and by which the closing time of at least one intake valvecan be set at a time after the piston is at the bottom dead center, withthe opening and closing times of the exhaust valve being set at a timewhen the piston is in the vicinity of the bottom dead center, and thisvalve driving device can recirculate part of the exhaust gas into intakegas under a light load by changing the phase of the cams on the secondcam shaft (the present structure shall be the second setting of theopening and closing times of the valves).

By the aforementioned structure, in the case of the first setting of theopening and closing times of the valves, under a heavy load, the engineoperates in an early closing Miller cycle with a low compression ratio,so that the exhaust gas recirculation is hardly conducted; and under alight load, the engine operates in a normal cycle with a highcompression ratio, so that the exhaust gas recirculation is conducted.In the case of the second setting of the opening and closing times ofthe valves, under a light load, the engine operates in a normal cyclewith a high compression ratio, so that the exhaust gas recirculation isconducted; and under a heavy load, the engine operates in a late closingMiller cycle with a low compression ratio, so that the exhaust gasrecirculation is hardly conducted.

Next, the second aspect of the variable compression ratio engine ischaracterized by including an intake device which changes the valvetiming of at least one of the intake valves by changing the phase of thecam for opening and closing the intake valve, to thereby set the closingtime of the intake valves at a time before the piston is at the bottomdead center, and to thereby, at a specified driving time, set theclosing time of at least one of the intake valves at a time when thepiston is in the vicinity of the bottom dead center. The closing time ofthe intake valves which is set at the time before the piston is at thebottom dead center can be at a time when a crank rotational angle is inthe range of 20° to 90° before the piston is at the bottom dead center.

By the aforementioned structure, at a specified driving time, forexample, at a starting time or under a light load, the compression ratiocan be increased, so that an excellent start or combustion state can besecured. When the closing time of the intake valves is set in the rangeof 20° to 90° before the piston is at the bottom dead center, thecompression ratio can be reduced, so that the pressure within a cylinderchamber at the end of the compression is lowered. Accordingly, a marginup to the maximum allowable pressure is made, so that high power can beoutputted.

Next, the third aspect of the variable compression ratio engine ischaracterized by including an exhaust gas recirculating device equippedwith a first cam shaft, provided with the cams operating the intakevalve and the exhaust valves, and the second cam shaft, provided withcams for operating at least one of the intake valves and the exhaustvalve; a planetary gear unit equipped with a sun gear, a ring gear whichis fixedly attached to the first cam shaft, a gear which is mcshed withthis ring gear and fixedly attached to the second cam shaft, and aplanet gear, and a variable valve timing device which changes the valvetiming by adjusting the phases of the first and the second cam shafts byfreely changing a relative positional relationship between a supportshaft of a planet gear and a shaft of the sun gear, so that part of theexhaust gas is recirculated into intake gas by operating the variablevalve timing device.

By the aforementioned structure, the relative positional relationshipbetween the support shaft of a planet gear and the shaft of the sun gearcan be changed to be a different positional relationship by operatingthe variable valve timing device. Accordingly, the phase of one camshaft can be changed with respect to the other cam shaft, so that theexhaust gas recirculating device can be operated. By this mechanicalstructure, the exhaust gas recirculation can be conducted when needed asin the first aspect of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a transverse cross-sectional view of a cylinder head portionof a diesel engine which is provided with the exhaust gas recirculatingdevice relating to the first embodiment of the present invention;

FIG. 2 is a longitudinal sectional view of the engine in FIG. 1;

FIG. 3 is a longitudinal sectional view of the exhaust gas recirculatingdevice of the engine along line X--X of FIG. 1;

FIG. 4 is a graph showing the relationship between the movement of thepiston and the opening areas of the intake and exhaust valves under aheavy load on the engine relating to the first embodiment;

FIG. 5 is a PV diagram for a heavy load on the engine relating to thefirst embodiment;

FIG. 6 is a graph showing the relationship between the movement of thepiston and the opening areas of the intake and exhaust valves under alight load on the engine relating to the first embodiment;

FIG. 7 is a PV diagram for a light load on the engine relating to thefirst embodiment;

FIG. 8 is a graph showing the relationship between the variation of thecompression ratio and the load on the engine relating to the firstembodiment;

FIG. 9 is a graph showing the relationship between the variation of theEGR rate and the load on the engine relating to the fist embodiment;

FIG. 10 is a transverse cross-sectional view of a cylinder head of agasoline engine provided with the exhaust gas recirculating devicerelating to the second embodiment of the present invention;

FIG. 11 is a longitudinal sectional view of the engine in FIG. 10;

FIG. 12 is a longitudinal sectional view of the exhaust valve drivingdevice of the engine along line Y--Y of FIG. 10;

FIG. 13 is a graph showing the relationship between the movement of thepiston and the opening areas of the intake and exhaust valves when alight load is on the engine relating to the second embodiment;

FIG. 14 is a graph showing the relationship between the movement of thepiston and the opening areas of the intake and exhaust valves when aheavy load is on the engine relating to the second embodiment;

FIG. 15 is a PV diagram when a heavy load is on the engine relating tothe second embodiment;

FIG. 16 is a transverse cross-sectional view of a cylinder head portionof the diesel engine relating to the third embodiment of the presentinvention;

FIG. 17 is a longitudinal sectional view of the engine in FIG. 16;

FIG. 18 is a graph showing the relationship between the movement of thepiston and the opening areas of the intake and exhaust valves when aheavy load is on the engine relating to the third embodiment;

FIG. 19 is a graph showing the relationship between the movement of thepiston and the opening areas of the intake and exhaust valves when theengine is started and when a light load is on the engine relating to thethird embodiment;

FIG. 20A and FIG. 20B are PV diagrams for comparing the PV diagramsrelating to the third embodiment, wherein FIG. 20A shows the PV diagramwhen the engine is started and under a light load and FIG. 20B shows thePV diagram under a heavy load;

FIG. 21 is a transverse cross-sectional view of a cylinder head portionof the gasoline engine relating to the fourth embodiment of the presentinvention;

FIG. 22 is a longitudinal sectional view of the engine in FIG. 21;

FIG. 23 is a graph showing the relationship between the movement of thepiston and the opening areas of the intake and exhaust valves when theengine is started and a light load is on the engine relating to thefourth embodiment;

FIG. 24 is a graph showing the relationship between the movement of thepiston and the opening areas of the intake and exhaust valves when aheavy load is on the engine relating to the fourth embodiment;

FIG. 25 is an elevational view showing the gear train of the variablevalve timing device relating to the fifth embodiment of the presentinvention;

FIG. 26 is a sectional view along line Z--Z of FIG. 25;

FIG. 27 is a graph showing an average axial effective pressure, etc., ata specified compression ratio of the engine relating to the conventionalart;

FIG. 28 is a general view of an early closing Miller cycle enginerelating to the conventional art; and

FIG. 29A and FIG. 29B show the relationship between the movement of thepiston and the opening areas of the intake and exhaust valves in theengine in FIG. 28, and FIG. 29A is a graph with a light load and FIG.29B is a graph with a heavy load.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferable embodiment of the variable compression ratio enginerelating to the present invention will be described below in detail withreference to the attached drawings.

FIG. 1 to FIG. 3 show a diesel engine, provided with the exhaust gasrecirculating device relating to the first embodiment, and each cylinderhas two intake valves and two exhaust valves. At a cylinder head 1, afirst intake valve 2, a second intake valve 3, a first exhaust valve 4,a second exhaust valve 5, a first cam shaft 10, and a second cam shaft20 are placed. At the first cam shaft 10, cams 11, 12, and 13 areprovided for the first intake valve 2, the first exhaust valve 4, andthe second exhaust valve 5, and the cam 12 directly operates the firstexhaust valve 4. The cams 11 and 13 respectively operate the firstintake valve 2 and the second exhaust valve 5 by the medium of rockerarms 14 and 15.

At the second cam shaft 20, cams 21 and 22 are provided, and the cam 21directly operates the second intake valve 3. The cam 22 operates therocker arm 15, by oscillating a lever 23 placed at the cylinder head 1with a pin 24 as its center, to open and close the second exhaust valve5. The second cam shaft 20 is rotated to an angle previously specifiedby a driving device, which is not illustrated in the drawings and whichcan change the phases of the cams 21 and 22. Thereby the valve timing ofthe second intake valve 3 and the second exhaust valve 5 can be delayed.25 is a piston, 26 and 27 are intake passages, and 28 is an exhaustpassage.

The operation by the aforementioned structure will be described.

In FIG. 4, the axis of abscissa shows the position of the piston 25, thesolid line shows the opening area of one valve, the two-dot chain lineshows the total opening areas of two valves, A1 shows one exhaust valve,B1 shows one intake valve, and C1 shows the second exhaust valve. Thefirst and second exhaust valves 4 and 5 start to open before the piston25 is at the bottom dead center and close when the piston 25 is in thevicinity of the top dead center, and always have the same phases. Thefirst and second intake valves 2 and 3 start to open when the piston 25is in the vicinity of the top dead center and close when the piston 25is in the vicinity of 90° before the bottom dead center, and have thesame phases. At the same time, the second intake valve 3 opens when thepiston 25 is in the vicinity of the top dead center, the second exhaustvalve 5 opens for a short time, as C1 shows. However, since the secondexhaust valve 5 opens when the piston 25 is in the vicinity of the topdead center, most of the exhaust gas does not recirculate into theintake gas, so that there is no possibility that the fuel consumptionincreases or that the output is reduced.

FIG. 5 shows the state under a heavy load, and in the intake stroke,intake is started at P0, and at P1a the first and the second intakevalves 2 and 3 close, so that the pressure within the cylinder decreasesand goes along the arrow to P1b. In the compression stroke, the pressurewithin the cylinder reaches P2a via P1b and P1a, in the combustion andexpansion strokes, the pressure goes to P3 from P2a and then to P4, andin the exhaust stroke, the pressure goes to P1c from P4 and then to P0.In short, the engine operates in an early closing Miller cycle. Atalmost the end of the intake stroke, only the expansion and compressionfrom P1a to P1b to P1a are conducted, so that the actual compressionratio is reduced to be as low as 11 to 13. Accordingly, high power canbe outputted.

On the other hand, when the load is light, the phases of the cams 21 and22 are changed, as in FIG. 1, by rotating the second cam shaft 20 by thedriving device, and the closing time of the second intake valve 3 is setat as late as the time when the piston 25 is in the vicinity of thebottom dead center. In FIG. 6, showing the variation of the opening areaunder a light load, B11 shows the first intake valve 2, and B12 showsthe second intake valve 3. Accordingly the second exhaust valve 5 is atthe position shown in C1, that is, in the vicinity of 90° before thepiston is at the bottom dead center, and exhaust gas is recirculatedinto the intake gas. As a result, the EGR rate becomes high, so that thegeneration of NOx is reduced.

FIG. 7 is a PV diagram under a light load, and the engine operates in anormal cycle with the intake stroke from P0 to P1, the compressionstroke from P1 to P2, the combustion stroke from P2 to P3, the expansionstroke from P3 to P4, and the exhaust stroke from P4 to P1 to P0. Thecompression ratio in this cycle is 15 to 17, and an excellent start andcombustion state can be obtained.

The relationship between the aforementioned load on the engine and thecompression ratio or the EGR rate will be described. In FIG. 8, the mostexternal curve is a torque curve when the engine outputs the maximumpower. As shown in the drawing, when the load becomes heavier, thecompression ratio becomes lower, in other words, when the load islighter, the compression ratio becomes higher. As shown in FIG. 9, whenthe load on the engine is lighter, the EGR rate becomes higher.

The second embodiment of the variable compression ratio engine relatingto the present invention will now be described in detail with referenceto the attached drawings.

FIG. 10 to FIG. 12 show the essential parts of the gasoline engineprovided with two intake and two exhaust valves per cylinder. At acylinder head 31, a first intake valve 32, a second intake valve 33, afirst exhaust valve 34, a second exhaust valve 35, a first cam shaft 40,and a second cam shaft 50 are placed. At the first cam shaft 40, thecams 41, 42, and 43 are provided for the first intake valve 32, thefirst exhaust valve 34, and the second exhaust valve 35. The cam 41operates the first intake valve 32 by the medium of a rocker arm 44, andthe cam 42 directly operates the first exhaust valve 34. The cam 43operates the second exhaust valve 35 by the medium of a lever 46attached at the cylinder head 31 by a pin 45 so as to be free tooscillate.

At a second cam shaft 50, cams 51 and 52 are provided, and the cam 51directly operates the second intake valve 33. The cam 52 oscillates thelever 46, by the medium of a lever 54 attached at the cylinder head 31by a pin 53 so as to be free to oscillate, to open and close the secondexhaust valve 35. The second cam shaft 50 is rotated to an anglepreviously specified by a driving device, which is not illustrated inthe drawing; and by changing the phases of the cams 51 and 52, the valvetiming of the second intake valve 33 and the second exhaust valve 35 canbe delayed. 55 is a piston, 56 and 57 are intake passages, and 58 is anexhaust passage.

The operation by the aforementioned structure will be described. FIG. 13shows the variation of the opening area when a load is light, and theaxis of abscissa shows the position of the piston 55, the solid lineshows the opening area of one valve, and the two-dot chain line showsthe total opening areas of two valves. A2 corresponds to one exhaustvalve, B2 corresponds to one intake valve, and C2 corresponds to thesecond exhaust valve. The first and second exhaust valves 34 and 35start to open before the piston 55 is at the bottom dead center, closewhen the piston 55 is in the vicinity of the top dead center, and havethe same phases. On the other hand the first and second intake valves 32and 33 have the same phases, and start to open when the piston 55 is inthe vicinity of the top dead center and close when the piston 55 is inthe vicinity of the bottom dead center. The second exhaust valve 35opens for a short time in the vicinity of 90° before the piston 55 is atthe bottom dead center, and exhaust gas is recirculated into the intakegas. Accordingly, the EGR rate increases and generation of NOx isreduced.

The cycle operation from the intake stroke to the exhaust stroke under alight load has the same basic cycle pattern as that in FIG. 7 of thefirst embodiment. The compression ratio in this cycle operation is inthe range of 11 to 13, so that the starting efficiency and thermalefficiency are improved, and the fuel consumption and generation of CO₂can be reduced.

FIG. 14 shows the variation of the opening area under a heavy load, andA2 corresponds to one exhaust valve, B21 corresponds to the first intakevalve 32, B22 corresponds to the second intake valve 33, and C2corresponds to the second exhaust valve 35. Under the aforementionedheavy load, the second cam shaft 50 is rotated by a driving device,which is not illustrated in the drawing, and the second intake valve 33closes at the position of 90° after the piston is at the bottom deadcenter. Accordingly, the second exhaust valve 35 opens and closes whenthe piston 55 is in the vicinity of the bottom dead center, so thatalmost none of the exhaust gas recirculates into the intake gas.Therefore an increase in fuel consumption and reduction of output can beprevented.

FIG. 15 is a PV diagram under a heavy load, and an intake of gas isconducted in the intake stroke from P0 to P1. In the compression stroke,the pressure does not increase from P1 to P1d since the second intakevalve 33 opens, and due to the result that the second intake valve 33closes at the point P1d, the pressure increases from P1d to P2b. To thisstroke, the combustion stroke from P2b to P3, the expansion stroke fromP3 to P4, and the exhaust stroke from P4 to P1 to P0 follow, and theengine operates in a late closing Miller cycle. The compression ratio atthis time is 8 to 10, so that the high power can be outputted and theoccurrence of knocking under a high output is prevented.

The third embodiment of the variable compression ratio engine relatingto the present invention will now be described in detail with referenceto the drawings.

FIG. 16 and FIG. 17 show a diesel engine having two intake valves andtwo exhaust valves for each cylinder, and at a cylinder head 101, afirst intake valve 102, a second intake valve 103, a first exhaust valve104, a second exhaust valve 105, a first cam shaft 110, and a second camshaft 120 are placed. At the first cam shaft 110, the cams 111, 112, and113 are provided for the first intake valve 102, the first exhaust valve104, and the second exhaust valve 105. The cam 112 directly operates thefirst exhaust valve 104, and the cams 111 and 113 operate the firstintake valve 102 and the second exhaust valve 105 by the medium ofrocker arms 114 and 115.

At a second cam shaft 120, a cam 121 is provided and directly operatesthe second intake valve 103. The second cam shaft 120 is rotated to anangle previously specified by a driving device, which is not illustratedin the drawings, and the valve timing of the second intake valve 103 canbe delayed by changing the phase of the cam 121. 122 is a piston, 123and 124 are intake passages, and 125 is an exhaust passage.

The operation by the aforementioned structure will be described.

FIG. 18 shows the variation of the opening area under a heavy load, theaxis of abscissa is the position of the piston 122, the solid line is anopening area of one valve, the two-dot chain line is the total openingareas of two valves. A3 corresponds to one exhaust valve, and B3corresponds to one intake valve. The first and second exhaust valves 104and 105 begin to open before the piston 122 is at the bottom dead centerand close when the piston 122 is in the vicinity of the top dead center.The phases are always the same. The first and the second intake valves102 and 103, which have the same phases, begin to open when the piston122 is in the vicinity of the top dead center and close in the vicinityof 20° to 90° before the piston 122 is at the bottom dead center.

The cycle operation from the intake stroke to the exhaust stroke under aheavy load has the same basic cycle pattern as that in FIG. 5 of thefirst embodiment, as shown in FIG. 20B. Accordingly the engine operatesin an early closing Miller cycle as in the first embodiment under aheavy load, and the actual compression ratio is as low as 11 to 13, sothat high power can be outputted.

On the other hand, at the starting time and under a light load, thephase of the cam 121 is changed by rotating the second cam shaft 120 bythe driving device, and the time when the second intake valve 103 closesis delayed to the time when the piston 122 is in the vicinity of thebottom dead center. In FIG. 19 showing the variation of the opening areain this case, B31 corresponds to the first intake valve 102, and B32corresponds to the second intake valve 103. Accordingly, the intakevalve 102 opens when the piston 122 is in the vicinity of the top deadcenter and the intake valve 103 close when the piston 122 is in thevicinity of the bottom dead center. From the intake stroke to theexhaust stroke, the basic cycle pattern becomes a nodal cycle operationwhich is the same as in FIG. 7 of the first embodiment and thecompression ratio is 15 to 17.

The difference between the aforementioned state under a heavy load andthe state at the starting time or under a light load will be describedwith reference to FIG. 20A and FIG. 20B. The compression ratio under aheavy load is as small as 11 to 13, so that the compression pressure P2ais lower than P2 and there is a margin up to P3, which is a maximumallowable pressure Pmax of the engine, therefore a lot of fuel can becombusted. As a result, the area surrounded by P1c to P1a to P2a to P3to P4 under a heavy load is larger than the area surrounded by P1 to P2to P3 to P4 at the starting time, etc. Accordingly the amount of workdone under a heavy load is large and high power is outputted, so that anengine with a small size and with a high output can be realized.Moreover, the intake part has no excessive volume, so that the enginecan operate in an efficient Miller cycle. On the other hand, at thestarting time and under a light load, the compression ratio is as largeas 15 to 17, so that an excellent start and combustion state can beobtained.

Next, the fourth embodiment of the variable compression ratio enginerelating to the present invention will be described in detail withreference to the drawings.

FIG. 21 and FIG. 22 show the gasoline engine provided with two intakeand two exhaust valves for each cylinder, and at a cylinder head 131, afirst intake valve 132, a second intake valve 133, a first exhaust valve134, a second exhaust valve 135, a first cam shaft 140, and a second camshaft 150 are placed. At the first cam shaft 140, the cams 141, 142, and143 are provided for the first intake valve 132, the first exhaust valve134, and the second exhaust valve 135. The cam 141 operates the firstintake valve 132 by the of a rocker arm 144, and the cams 142 and 143directly operate the first exhaust valve 134 and the second exhaustvalve 135.

At the second cam shaft 150, a cam 151 is provided and directly operatesthe second intake valve 133. The second cam shaft 150 is rotated to anangle previously specified by a driving device, which is not illustratedin the drawings and which can delay the valve timing of the secondintake valve 133 by changing the phase of the cam 151. 152 is a piston,153 and 154 are intake passages, and 155 is an exhaust passage.

The operation in the aforementioned structure will be described. In FIG.23, the solid line is an opening area of one valve, and the fine two-dotchain line shows the total opening areas of two valves, and A4corresponds to one exhaust valve and B4 corresponds to one intake valve.The first and second exhaust valves 134 and 135 begin to open before thepiston 152 is at the bottom dead center, close when the piston 152 is inthe vicinity of the top dead center, and always have the same phase. Thefirst intake valve 132 and the second intake valve 133 have the samephase, and begin to open when the piston 152 is in the vicinity of thetop dead center, then close when the piston 152 is in the vicinity ofthe bottom dead center.

From the intake stroke to the exhaust stroke at the starting time andunder a light load, the basic cycle pattern is the same normal cycleoperation as in FIG. 7 of the first embodiment, and the compressionratio is 11 to 13. Accordingly, like in the second embodiment, thestarting efficiency and thermal efficiency are improved, and the fuelconsumption and the generation of CO₂ can be reduced.

FIG. 24 shows the variation of the opening area under a heavy load, andB41 corresponds to the first intake valve 132, and B42 corresponds tothe second intake valve 133. Under the heavy load, the second cam shaft150 is rotated by a driving device, which is not illustrated in thedrawings, so that the second intake valve 133 closes at 40° to 90° afterthe piston is at the bottom dead center.

From the intake stroke to the exhaust stroke under a heavy load, thebasic cycle pattern is the same as in FIG. 15 of the second embodiment,and the engine operates in a late closing Miller cycle. Citing FIG. 15,in the compression stroke from P1 to P1d, the pressure doesn't increasesince the second intake valve 133 opens, and as the second intake valve133 closes at the point P1d, the pressure increases from P1d to P2b. Thecompression ratio at this time is 8 to 10, and a high power isoutputted, and the occurrence of knocking is prevented as in the secondembodiment. In addition, the intake part has no excessive volume, sothat the efficient variable compression ratio engine can be obtained.

Next, the fifth embodiment of the variable compression ratio enginerelating to the present invention will be described in detail withreference to the drawings.

The variable compression ratio engine of the present embodiment is adouble overhead camshaft type of engine which can convert between anormal cycle and a Miller cycle, and has the engine in the thirdembodiment as a base with the variable valve timing device beingprovided. In FIG. 16, the second cam shaft 120 can be rotated as shownby the arrows by the variable valve timing device described below. Bythis device, the valve timing can be changed to a degree in the range of70° to 90° for the crankshaft angle, so that the actual compressionratio is variable and high power can be outputted.

The aforementioned variable valve timing device will be described. FIG.25 and FIG. 26 show a gear train placed at the end portions of the firstand second cam shafts 110 and 120 in FIG. 16. 230 is a sun gear fixedlyattached to the first cam shaft 110, and 231 is a ring gear attached tothe foremost end of the first cam shaft 110 by the medium of a bearing232 so as to be free to rotate. The ring gear 231 is provided with aninternal gear 233 and an external gear 234. 235 is a planet gear whichis meshed with the sun gear 230 and the internal gear 233, 236 is asupport shaft of the planet gear 235, and 237 is a carrier to which thesupport shaft 236 is fixedly attached. The carrier 237 is attached tothe cylinder head 101 by a shaft so as to freely rotate, and a wormwheel 238 of a sector form is provided at the outer perimeter. The wormwheel 238 is meshed with a worm 241, which is driven by an electricmotor 240.

At the second cam shaft 120 supported by a shaft at the cylinder head101, a gear 242, which is meshed with the external gear 234, and atiming gear 243 are fixedly attached. The timing gear 243 is meshed witha crank gear 246 fixedly attached to a crankshaft 245 by the medium ofan idle gear 244.

Here, when the number of teeth of the sun gear 230 is Z1, the number ofteeth of the internal gear 233 of the ring gear 231 is Z2, the number ofteeth of the gear 242 is Z3, and the number of teeth of the externalgear 234 of the ring gear 231 is Z4, wherein Z1 / Z2=Z3 / Z4. The ratioof the numbers of teeth of the crank gear 246 and the timing gear 243 is1/2. Accordingly, the rotational speed of the second cam shaft 120 is1/2 of the rotational speed of the crankshaft 245, and the second camshaft 120 and the first cam shaft 110 have the same rotational speed.

The operation by the aforementioned structure will now be described.When the phase of the first cam shaft 110 and the second cam shaft 120is changed, the worm 241 is rotated by the electric motor 240, and theworm wheel 238 is rotated to a specified angle. The carrier 237 rotatesat the same time, since the carrier 237 is integrated with the wormwheel 238, and the planet gear 235 rotates the ring gear 231 byrevolving around the sun gear 230 as the planet gear 235 is rotating.Accordingly, the gear 242 rotates, and the phase of the second cam shaft120 to the first cam shaft 110 is changed. The rotational angle ratio γof the gear 242 and the worm wheel 238 at this time can be obtained fromthe following formula.

    γ= (Z1+Z2)/Z2!z4/Z3

Accordingly, the variable valve timing device, in which the gear 242rotates at a large angle only by rotating the worm wheel 238 at a smallangle, can easily give a phase difference in the range of 70° to 90°between the first cam shaft 110 and the second cam shaft 120.

Summing up the aforementioned present embodiments, two cam shafts areconnected by the medium of a planetary gear unit consisting of the sungear, ring gear and the planet gear, and one cam shaft is fixedlyattached to the sun gear while the other cam shaft is fixedly attachedto a gear which is meshed with the ring gear. The carrier supporting theplanet gear is rotatably attached to a case supporting the sun gearshaft, and is connected to a rotational driving device. Accordingly, therotational speed of the gear meshed with the ring gear is increased,relative to the rotation of the carrier. In other words, when thecarrier is rotated over a small angle by the rotational driving device,the gear is rotated over a large angle.

INDUSTRIAL AVAILABILITY

The present invention is useful as a variable compression ratio engine,which can convert between an early closing or a late closing Millercycle operation and a normal cycle operation, and which can reduce thegeneration of NOx, etc., and can prevent the occurrence of knocking.

I claim:
 1. A variable compression ratio engine for operating in a firstcondition under a heavy load and in a second condition under a lightload, said engine comprising:at least one cylinder chamber; at least onepiston, each piston being positioned in a respective cylinder chamber;first and second intake valves per cylinder chamber; at least oneexhaust valve per cylinder chamber; a first cam shaft provided with camsfor opening and closing said first intake valve and said at least oneexhaust valve; a second cam shaft provided with cams for opening andclosing said second intake valve and at least one of said at least oneexhaust valve; and a device for changing a phase, between cams on saidsecond cam shaft and cams on said first cam shaft, between a first phasefor operating in said first condition under a heavy load and a secondphase for operating in said second condition under a light load; wherebya compression ratio of said engine can be changed by changing a timingof the opening and closing of said intake valves and/or said at leastone exhaust valve; whereby, in an intake stroke during said firstcondition under a heavy load, said device sets said intake valves toclose at a time before the respective piston is at a bottom dead centerof its cycle, and said device sets at least one of said at least oneexhaust valve to open and close at times when the respective piston isin the vicinity of a top dead center of its cycle; and whereby, in anintake stroke during said second condition under a light load, saiddevice sets at least one of said intake valves to close at a time whenthe respective piston is in the vicinity of the bottom dead center ofits cycle, and said device sets at least one of said at least oneexhaust valve to open and close at times before the respective piston isat the bottom dead center of its cycle so as to recirculate part of theexhaust gas from said cylinder chamber into intake gas for said cylinderchamber.
 2. A variable compression ratio engine in accordance with claim1, wherein said at least one exhaust valve comprises first and secondexhaust valves;wherein said first cam shaft is provided with cams foropening and closing said first intake valve and said first and secondexhaust valves; and wherein said second cam shaft is provided with camsfor opening and closing said second intake valve and said second exhaustvalve.
 3. A variable compression ratio engine in accordance with claim1, wherein said device comprises:a planetary gear unit provided with asun gear, a ring gear, and a planet gear, said sun gear being fixedlyattached to said first cam shaft; a gear which is meshed with said ringgear and fixedly attached to said second cam shaft; a support shaft forsaid planet gear; and a driving device for changing a relativepositional relationship between said support shaft for said planet gearand said first cam shaft.
 4. A variable compression ratio engine inaccordance with claim 1, wherein said time before the respective pistonis at a bottom dead center of its cycle is a time when a crankrotational angle is in the range of 20° to 90° before the respectivepiston is at the bottom dead center of its cycle.
 5. A variablecompression ratio engine for operating in a first condition under aheavy load and in a second condition under a light load, said enginecomprising:at least one cylinder chamber; at least one piston, eachpiston being positioned in a respective cylinder chamber; first andsecond intake valves per cylinder chamber; at least one exhaust valveper cylinder chamber; a first cam shaft provided with cams for openingand closing said first intake valve and said at least one exhaust valve;a second cam shaft provided with cams for opening and closing saidsecond intake valve and at least one of said at least one exhaust valve;and a device for changing a phase, between cams on said second cam shaftand cams on said first cam shaft, between a first phase for operating insaid first condition under a heavy load and a second phase for operatingin said second condition under a light load; whereby a compression ratioof said engine can be changed by changing a timing of the opening andclosing of said intake valves and/or said at least one exhaust valve;whereby, in an intake stroke during said second condition under a lightload, said intake valves are set to close at a time when the respectivepiston is in the vicinity of a bottom dead center of its cycle, and atleast one of said at least one exhaust valve is set to open and close attimes before the respective piston is at the bottom dead center of itscycle so as to recirculate part of the exhaust gas from said cylinderchamber into intake gas for said cylinder chamber; and whereby, in anintake stroke during said first condition under a heavy load, at leastone of said intake valves is set to close at a time after the respectivepiston is at the bottom dead center of its cycle, and at least one ofsaid at least one exhaust valve is set to open and close at times whenthe respective piston is in the vicinity of the bottom dead center ofits cycle.
 6. A variable compression ratio engine in accordance withclaim 5, wherein said at least one exhaust valve comprises first andsecond exhaust valves;wherein said first cam shaft is provided with camsfor opening and closing said first intake valve and said first andsecond exhaust valves; and wherein said second cam shaft is providedwith cams for opening and closing said second intake valve and saidsecond exhaust valve.
 7. A variable compression ratio engine inaccordance with claim 5, wherein said device comprises:a planetary gearunit provided with a sun gear, a ring gear, and a planet gear, said sungear being fixedly attached to said first cam shaft; a gear which ismeshed with said ring gear and fixedly attached to said second camshaft; a support shaft for said planet gear; and a driving device forchanging a relative positional relationship between said support shaftfor said planet gear and said first cam shaft.
 8. A variable compressionratio engine in accordance with claim 5, wherein said time before therespective piston is at a bottom dead center of its cycle is a time whena crank rotational angle is in the range of 20° to 90° before therespective piston is at the bottom dead center of its cycle.
 9. Avariable compression ratio engine for operating under a first conditionor under a second condition, said engine comprising:at least onecylinder chamber; at least one piston, each piston being positioned in arespective cylinder chamber; first and second intake valves per cylinderchamber; at least one exhaust valve per cylinder chamber; a first camshaft provided with cams for opening and closing said first intake valveand said at least one exhaust valve; a second cam shaft provided with acam for opening and closing said second intake valve; and an intakedevice for changing a phase, between said cam on said second cam shaftand cams on said first cam shaft, between a first phase for operating insaid first condition and a second phase for operating in said secondcondition; whereby a compression ratio of said engine can be changed bychanging a timing of the opening and closing of said intake valvesand/or said at least one exhaust valve; whereby, in an intake strokeduring said first condition, said intake valves are set to close at atime before the respective piston is at a bottom dead center of itscycle; and whereby, in an intake stroke during said second condition, atleast one of said intake valves is set to close at a time when therespective piston is in the vicinity of the bottom dead center of itscycle.
 10. A variable compression ratio engine in accordance with claim9, wherein said time before the respective piston is at a bottom deadcenter of its cycle is a time when a crank rotational angle is in therange of 20° to 90° before the respective piston is at the bottom deadcenter of its cycle.
 11. A variable compression ratio engine inaccordance with claim 9, wherein said at least one exhaust valvecomprises first and second exhaust valves;wherein said first cam shaftis provided with cams for opening and closing said first intake valveand said first and second exhaust valves; and wherein said second camshaft is provided with said cam for opening and closing said secondintake valve.
 12. A variable compression ratio engine in accordance withclaim 9, wherein said device comprises:a planetary gear unit providedwith a sun gear, a ring gear, and a planet gear, said sun gear beingfixedly attached to said first cam shaft; a gear which is meshed withsaid ring gear and fixedly attached to said second cam shaft; a supportshaft for said planet gear; and a driving device for changing a relativepositional relationship between said support shaft for said planet gearand said first cam shaft.
 13. A variable compression ratio engine foroperating in a first condition or in a second condition, said enginecomprising:at least one cylinder chamber; at least one piston, eachpiston being positioned in a respective cylinder chamber; first andsecond intake valves per cylinder chamber; at least one exhaust valveper cylinder chamber; a first cam shaft provided with cams for openingand closing said first intake valve and said at least one exhaust valve;a second cam shaft provided with cams for opening and closing saidsecond intake valve and at least one of said at least one exhaust valve;a planetary gear unit provided with a sun gear, a ring gear, and aplanet gear, said sun gear being fixedly attached to said first camshaft; a gear which is meshed with said ring gear and fixedly attachedto said second cam shaft; a support shaft for said planet gear; and avariable valve timing device which changes valve timing by adjusting aphase, between said first and second cam shafts, between a first phasefor operating in said first condition and a second phase for operatingin said second condition, by freely changing a relative positionalrelationship between said support shaft for said planet gear and saidfirst cam shaft, whereby a compression ratio of said engine can bechanged by changing said valve timing and a part of exhaust gas fromsaid cylinder chamber is recirculated into intake gas for said cylinderchamber during said second condition.